In the cultivation of plants, e.g. vegetables, with balled seedlings, the aim is to obtain a complete stand of plants in the field. For various reasons, after the germination stage the seedling trays usually contain a number of balls without seedlings. These deficient balls were earlier sorted out manually before mechanical transplanting, or alternatively they were replaced with seedling-carrying balls following transplanting. In practice, the consequence of this is that the planting process is semiautomatic, whereby an operator supplies the machine only with seedling-carrying balls. Alternatively, automatic transplanting is first used, whereby the deficient balls are set in the ground and a person walking behind the machine manually replaces the deficient balls with seedling-carrying ones. This partly eliminates the economical benefit gained by the use of a continuously operating transplanting machine. If sorting or replacement is not carried out, the result is a patchy field and crop losses.
Japanese patent application 8-103112 discloses a device for removal of deficient seedling balls and replacement with seedling-carrying balls during automatic transplanting. The device is provided with a seedling feed unit wherein seedling balls are transferred to a carousel-type observation device, where individual balls are tested for the presence of a seedling using a detector. If the seedling is found absent, a replacement seedling is directed into the planting chute from a separate replacement seedling supply device.
Japanese patent application 8-112012 discloses a transplanting device, where seedling balls are fed from a cultivating tray for automatic transplanting, balls are tested by means of a detector, and when a seedling is found absent, a replacement seedling is extracted from a second, adjacent tray by means of a parallel mechanism.